Prior art vacuum flange O-ring centering rings are typically constructed from aluminum or stainless steel, and are designed to hold an elastomeric O-ring in position during the assembly and use of ISO-NW vacuum sealing flanges for tubing connections. Such centering rings only function to hold the O-ring in position for sealing to the flat sealing surfaces of the flanges and to prevent the O-ring from moving inward when gas pressure inside the tubing is lower than the gas pressure outside the tubing.
Two major shortcomings are associated with prior art centering ring designs. The shortcoming has to do with the diameter of the inner surface of the centering ring not matching the diameter of the inner surface of typical vacuum tubing and like components with ISO-NW vacuum flange connections. This shortcoming produces a stepped inner surface at the tubing (or component) connection. The stepped inner surface produces a turbulent gas flow effect, known as sudden expansion and/or sudden contraction (Vena contracta). The viscous flow of gases through this type of tubing connection will have turbulent flow with eddy current flow and total gas flow losses. This shortcoming can cause gas phase reactions, condensation, and premature clogging in some types of machinery gas piping.
The other shortcoming associated with prior art centering ring designs has to do with their "straight edge" outer surface design. The outer annular side surface of present centering rings are perpendicular to the annular face surfaces of the ring. This produces a 90 degree ring shoulder which mates with the counter bore area of the sealing flange. The 90 degree ring shoulder of prior art centering ring designs require the sealing surfaces of the sealing flanges to be aligned nearly parallel with each other when assembling the centering ring and the vacuum tubing, to prevent binding.
Accordingly, a need exists for an improved vacuum flange O-ring centering ring that substantially eliminates the turbulent gas flow and binding problems of prior art vacuum flange O-ring centering ring designs.